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INTERHEMISPHERIC COLLABORATION
DURING DUAL-TASK STIMULUS MATCHING
by
Urvi Jitendra Patel
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PSYCHOLOGY)
December 2008
Copyright 2008 Urvi Jitendra Patel

It is generally advantageous to spread information processing across both cerebral hemispheres as tasks become more complex. The present series of five experiments were designed to investigate whether introduction of a secondary task within a novel dual-task paradigm influences the pattern of interhemispheric collaboration without increasing the complexity of a primary comparison task. Recent research suggests that the advantage of spreading processing across both hemispheres is predicted to the extent that stimuli to be compared are likely to be processed in similar cortical pathways. To test how degree of cortical access route overlap may modulate hemispheric communication (CAR model), careful selection of primary and secondary stimulus formats was conducted.; For each of the five experiments of the present investigation, observers engaged in the following three types of conditions: (1) three-item comparison task (single primary task), (2) two-item comparison task (single secondary task), (3) three and two-item comparison task (dual-task). The critical comparison involved dual-task primary trials on which the two matching stimuli projected to the same visual field (within-hemisphere trials) versus trials on which the two matching stimuli projected to opposite visual fields (across-hemisphere trials). The results of Experiments 1 (all letters) and 2 (letters and pictures) showed support of the CAR model because an absent across-hemisphere advantage was established during the single primary task and neural overlap explained the across-hemisphere advantage found for the dual-task primary trials of the former but not the latter experiment. Experiments 3 to 5 involved a new application of the dimensions of numerical magnitude, physical size, and luminance to a dual-task paradigm. As an unexpected across-hemisphere advantage was found during the single primary task of experiments, interpretation of performance during the dual-task condition is limited. The results of Experiments 1 and 2 support the CAR model while the surprising findings of Experiments 3 to 5 do not provide an opportunity to test the model.

INTERHEMISPHERIC COLLABORATION
DURING DUAL-TASK STIMULUS MATCHING
by
Urvi Jitendra Patel
A Dissertation Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PSYCHOLOGY)
December 2008
Copyright 2008 Urvi Jitendra Patel